1. Field of the Invention
The present invention relates to a switching apparatus having electrodes which can be placed into and out of contact with each other for opening and closing a pair of electrodes, and more particularly, it relates to improving the efficiency in driving a switching apparatus with electromagnetic repulsion.
2. Description of the Related Art
FIGS. 8(a) and 8(b) show something analogous to a conventional switching apparatus utilizing electromagnetic repulsion which is, for example, described in speech No. 260 entitled "Switching Characteristic of Novel High-Speed Switch." The speech was made at the Japanese National Convention of the Department of Industrial Application of the Electric Society at the year of 1996.
In FIGS. 8(a) and 8(b), a switching apparatus includes a switch 1 having a movable electrode 5 and a stationary electrode 6 which can be placed into and out of contact with each other, a repulsion unit 2, an opening coil 3a for inducing current in the repulsion unit 2, a closing coil 3b for inducing a current in the repulsion unit 2, a movable shaft 4 coupled to the movable electrode 5, a terminal 7 connected to the movable electrode 5 and the stationary electrode 6, a pair of pressurizing springs 8a, 8b for urging the movable electrode 5 in a direction to contact the stationary electrode 6 through the movable shaft 4, and an auxiliary switch 9 operably connected with the switch 1 through the movable shaft 4. The repulsion unit 2 and the movable electrode 5 are fixedly coupled to the movable shaft 4, and disposed in a concentric relation to the electrodes. The opening coil 3a and the closing coil 3b are connected to a current supply (not shown) for generating magnetic fields. Moreover, the movable shaft 4 passes through a support member S for sliding movement relative thereto. The support member S supports the opening coil 3a and the closing coil 3b in opposition to each other with the repulsion unit 2 disposed therebetween.
In this connection, note that FIG. 8(a) shows a closed state of the movable and stationary coils 6a, 6b, while FIG. 8(b) shows an open state of them.
Moreover, FIG. 9 shows the load characteristics of the pressurizing springs 8a and 8b and a combined load thereof. Reference numeral 40 denotes the load characteristic of the pressurizing spring 8a, and 41 denotes the load characteristics of the pressurizing spring 8b. Reference numeral 42 denotes the combined load of the pressurizing springs 8a and 8b.
The pressurizing springs 8a and 8b are so arranged as to generate a combined load 42. Specifically, as shown in FIG. 9, the pressurizing springs 8a and 8b generate a load in a direction to close the movable and stationary contacts 5, 6 of the switch 1 within a range of deflection from an intermediate position to a closed position of the combined load. Another load will be generated in a direction to open the movable and stationary contacts 5, 6 of the switch within a range of deflection from the intermediate position to an open position of the combined load.
Next,an opening action for the switch 1 will be described. In a closed state of the switch 1 shown in FIG. 8(a), a pulsating current flows from the magnetic field generation current supply (not shown) into the opening coil 3a. This causes an induction current to flow into the repulsion unit 2, thereby inducing magnetic fields in a direction opposite magnetic fields generated by the opening coil 3a.
Due to the interaction between the magnetic fields induced by the opening coil 3a and the magnetic fields induced by the repulsion unit 2, the repulsion unit 2 undergoes electromagnetic repulsion to repulse the opening coil 3a.
Due to the electromagnetic repulsion, the movable shaft 4 and the movable electrode 5 fixed to the repulsion unit 2 together act in a direction of repulsion, so that In FIG. 9, the magnitude of deflection of the pressurizing spring 8a is changed from a value permitting the spring to lie at the closed position, to a value permitting the spring to lie at the intermediate position. With the change in the magnitude of deflection, the load characteristic 42 of the pressurizing spring 8a deteriorates. When the pressurizing spring 8a warps to go beyond the intermediate position, the load characteristic 42 provides a load oriented in a direction of opening. When the magnitude of warp assumes a value permitting the spring to lie at the open position, the switch 1 remains open as shown in FIG. 8(b).
Next, a closing action will be described. In an open state of the switch shown in FIG. 8(b), when a pulsating current flows into the closing coil 3b, magnetic fields are induced therein. This causes an induction current to flow into the repulsion unit 2. Thus, the repulsion unit 2 undergoes electromagnetic repulsion to repulse the closing coil 3b. Due to the electromagnetic repulsion, the movable shaft 4 and the movable electrode 5 fixed to the repulsion unit 2 act in the direction of repulsion. In FIG. 9, the magnitude of deflection of the pressurizing spring 8b changes from a value permitting the spring to lie at the closed position to a value permitting it to lie at the intermediate position. With the change in the magnitude of deflection, the load characteristic 42 improves. When the pressurizing spring 8b is deflected to go beyond the intermediate position, the load characteristic 42 provides a load oriented in a direction of closing. When the magnitude of deflection assumes a value permitting the spring to lie at the closed position, the switch 1 is closed as shown in FIG. 8(a).
In the conventional switching apparatus, as mentioned above, the magnetic field strength provided by the repulsion unit 2 due to induction is smaller than that provided by supplying current directly to an electric circuit. Consequently, electromagnetic repulsion stemming from the interaction between magnetic fields induced by a coil and those induced in the repulsion unit does not occur effectively. Moreover, in order to increase the magnetic field strength, the number of turns of the coil has to be increased, or pulsating current output has to be increased, thus requiring a large power supply. This poses a problem in that an entire device has to be designed on a large scale.
Moreover, in the conventional switching apparatus, high driving efficiency is realized by utilizing electromagnetic repulsion derived from the interaction between magnetic fields induced by the coils and those induced in the repulsion unit. When an opening or closing action is carried out, it becomes necessary for each coil to receive the supply of pulsating current from a power supply. This is disadvantageous in terms of costs and compactness of the device.